增加ETag为实体的验证提供了一个比使用“last - modified date(上次编辑时间)”更加灵活的机制。

(an "entity" is another word a "component" : images, scripts, stylesheets, etc.) ETags were added to provide a mechanism for validating entities that is more flexible than the last-modified date.

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这表明，自上次保存以来，编辑器已经被修改。

This indicates the editor has been changed since the last time it was saved.

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